JP3850163B2 - Multilayer piezoelectric actuator and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer piezoelectric actuator, for example, a multilayer piezoelectric actuator used for a precision positioning device such as an optical device, a driving element for vibration prevention, a driving element for fuel injection of an automobile engine, and the like. is there.
[0002]
[Prior art]
Conventionally, a piezoelectric plate has an inverse piezoelectric effect that expands and contracts when a voltage is applied. However, since the amount of expansion / contraction of each piezoelectric plate is very small, a stacked piezoelectric actuator formed by stacking a plurality of piezoelectric plates has been manufactured.
[0003]
In this laminated piezoelectric actuator, a voltage is applied to a piezoelectric plate and extended by several to several tens of μm, and used as a driving force source for the actuator. Known examples include Japanese Patent Publication No. 7-40613.
[0004]
In such a laminated piezoelectric actuator, for example, a conductive adhesive layer having a thickness of several μm is formed on both surfaces of a piezoelectric plate by a method such as printing or vapor deposition, and this conductive adhesion is performed. It consists of a structure in which a thin metal plate is interposed between the layers and thermocompression bonded and integrated.
[0005]
As such a laminated piezoelectric actuator, for example, according to Japanese Patent Laid-Open No. 60-121784, a conductive adhesive layer formed by printing and baking a mixed paste of Ag powder and glass powder on both sides is formed. A plurality of piezoelectric plates are stacked with a thin metal plate placed between the conductive adhesive layers, and the connection protrusions formed on the thin metal plate are bent in the axial direction so as to leave a predetermined gap with respect to the outer peripheral surface of the piezoelectric plate. In addition, a multilayer piezoelectric actuator in which connecting protrusions having the same polarity are overlapped and joined by spot welding or the like is disclosed.
[0006]
In addition, Japanese Utility Model Publication No. 60-3589 discloses a ribbon-shaped metal plate that does not require soldering, in which thin metal plates are connected by a connecting member, and a laminated piezoelectric material using such a ribbon-shaped metal plate. A large number of actuators have been proposed (see Japanese Patent Laid-Open Nos. 60-10385, 61-276278, 4-16029, and Japanese Patent Laid-Open No. 7-283455).
[0007]
In recent years, a multilayer piezoelectric actuator is driven by applying a high voltage at a high frequency in order to utilize the high response characteristic of the multilayer piezoelectric actuator while securing a large amount of displacement. In addition, a thinner piezoelectric plate is used to promote further miniaturization.
[0008]
[Problems to be solved by the invention]
However, in the laminated piezoelectric actuator in which a conductive adhesive layer is formed on both surfaces of the piezoelectric plate disclosed in Japanese Patent Publication No. 7-40613, and the piezoelectric plate and the metal thin plate are thermocompression bonded through the conductive adhesive layer, When laminating a piezoelectric plate and a thin metal plate, the conductive thin layer on the surface of the piezoelectric plate and the thin metal plate are displaced from each other. Therefore, when driving with a high voltage and a high frequency is performed, Due to the expansion and contraction operation in the radial direction accompanying the displacement, the stress generated at the joint between the piezoelectric plate and the metal thin plate becomes non-uniform, and high stress is generated at the misalignment portion between the conductive adhesive layer on the piezoelectric plate and the metal thin plate, There was a problem that a crack occurred in the piezoelectric plate during driving, and the reliability of the actuator was lowered.
[0009]
In addition, when a multilayer piezoelectric actuator is installed in a device with a high load applied, stress concentration due to the load occurs at the misaligned portion of the conductive adhesive layer and the metal thin plate, promoting the occurrence of cracks in the piezoelectric plate. It was.
[0010]
Furthermore, a laminated piezoelectric actuator disclosed in Japanese Patent Application Laid-Open No. 59-218784 in which connection protrusions of the same polarity are overlapped and joined with solder, or a ribbon-shaped metal plate that does not need to be joined with solder or the like is used. In a laminated piezoelectric actuator such as 7-283455, when a metal with a low Young's modulus is used as the metal thin plate, the connection protrusion and the connecting portion of the ribbon-shaped metal plate are easily deformed, and the connection protrusion is deformed by the displacement operation. In a stacked piezoelectric actuator in which stress concentration occurs at the joints and fatigue breakage occurs, or connection projections of the same polarity are overlapped and joined by spot welding, the joints are damaged due to high stress accompanying high displacement. There was a problem of fatigue and easy breakage.
[0011]
In addition, when bonding is performed through a conductive adhesive layer made of Ag and glass disclosed in JP-A-60-121784, the glass component preferentially diffuses into the ceramic grain boundary of the piezoelectric body during thermocompression bonding. Electrical characteristics and durability were deteriorated.
[0012]
As means for solving these problems, Japanese Patent Publication No. 7-118554 discloses a method of manufacturing a laminated piezoelectric actuator without pressing a metal thin plate and a piezoelectric plate. According to this, a relatively hard material such as stainless steel is used as the metal thin plate, and electrode materials such as copper, silver, and aluminum that are softer than the metal thin plate are formed on both surfaces of the metal thin plate by a method such as plating. Later, when the soft electrode formed on the electrode thin plate and the piezoelectric plate come into contact with each other, the piezoelectric plate functions as an electrode of the piezoelectric plate, and voltage application to the piezoelectric plate becomes possible.
[0013]
However, in such a laminated piezoelectric actuator, the piezoelectric plate and the metal thin plate are not substantially joined, and it is difficult to maintain the laminated state. For this reason, the laminated piezoelectric actuator having this structure has to be sealed in a case immediately after lamination, and handling in the process is very difficult.
[0014]
Accordingly, an object of the present invention is to provide a highly reliable stacked piezoelectric actuator that can reliably connect a piezoelectric plate and a thin metal plate and that prevents cracks in the piezoelectric plate.
[0015]
[Means for Solving the Problems]
As a result of repeated studies on the above problems, the present inventors have found that the surface of the metal thin plate is a laminated piezoelectric actuator formed by alternately laminating a plurality of piezoelectric plates and a plurality of metal thin plates. An Ag metal layer substantially free of glass is coated, and the Ag metal layer is press-fitted between crystal grains on the surface of the ceramic piezoelectric plate, thereby bonding the ceramic piezoelectric plate and the metal thin plate to the Ag. It is characterized by being joined and integrated through a metal layer.
[0016]
In addition, as a method for manufacturing such a multilayer piezoelectric actuator, a plurality of ceramic piezoelectric plates and a metal thin plate having an Ag metal layer substantially free of glass formed on both surfaces are alternately laminated, and then 700 Heating at a temperature of 400 to 700 ° C. while applying a load of ˜2000 kgf, and press-fitting the Ag metal layer between crystal grains on the surface of the ceramic piezoelectric plate, thereby bringing the ceramic piezoelectric plate and the metal thin plate into the Ag It is characterized by being joined and integrated through a metal layer.
[0017]
In the above configuration, the metal thin plate is preferably made of an alloy containing Ni—Fe as a main component, and the thickness of the Ag metal layer is preferably 1 μm or more.
[0018]
[Action]
According to the multilayer piezoelectric actuator of the present invention, after alternately laminating a plurality of ceramic piezoelectric plates and thin metal plates having an Ag metal layer formed on both surfaces, a temperature of 400 to 700 ° C. is applied while applying a load of 700 to 2000 kgf. As shown in the schematic diagram of the bonding interface between the ceramic piezoelectric plate and the Ag metal layer in FIG. 4, the Ag metal layer coated on both surfaces of the thin metal plate is formed between the crystal grains on the surface of the ceramic piezoelectric plate. By being press-fitted into the ceramic piezoelectric plate, the ceramic piezoelectric plate is firmly joined and integrated with the metal thin plate via the Ag metal layer, and the laminated piezoelectric actuator obtains a bonding strength that can sufficiently withstand handling in the process. Can do. Since the conductive adhesive layer is not formed on the ceramic piezoelectric plate, the process can be simplified.
[0019]
In addition, since the conductive adhesive layer is not formed on the piezoelectric plate side, there is no problem of displacement of the conductive adhesive layer and the metal thin plate which has occurred during the above-described lamination, and the device can be applied by applying a high load. The concentration of stress on the misalignment between the conductive adhesive layer and the metal thin plate due to the incorporation of or driving at a high voltage and high frequency can be reduced. For this reason, generation | occurrence | production of the crack in the piezoelectric plate which generate | occur | produced with stress concentration can be suppressed.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
The multilayer piezoelectric actuator of the present invention has a basic structure in which a plurality of ceramic piezoelectric plates 1 and a plurality of thin metal plates 2 are alternately stacked, as shown in the schematic diagram of FIG.
[0021]
The ceramic piezoelectric plate 1 is generally made of ceramics mainly composed of Pb (ZrTi) O ₃ (hereinafter abbreviated as PZT). However, the ceramic piezoelectric plate 1 is not limited to this and may be any ceramic having piezoelectricity. anything is fine. As the piezoelectric material constituting the piezoelectric plate 1, those piezoelectric strain constant d ₃₃ is high is preferable. In particular, a piezoelectric ceramic composition made of a composite perovskite compound containing at least one of Zn, Sb, Ni, Te, Sr and Ba in addition to Pb, Zr and Ti as a metal component is desirable.
[0022]
The thickness t of the ceramic piezoelectric plate 1 is preferably 0.2 to 0.6 mm from the viewpoint of downsizing and applying a high voltage.
[0023]
The metal thin plate 2 includes a disk-shaped positive electrode metal thin plate 2a and a negative electrode metal thin plate 2b, and these metal thin plates 2a and 2b are alternately laminated. Moreover, as shown in the connection structure of the thin metal plates in FIG. 3, the thin metal plates 2 are connected in series by being connected by connecting members 3 (3a, 3b) for each polarity. As shown in FIGS. 1 and 2, the thin metal plates 2 connected in series are bent at the connecting portions 3 protruding in the radial direction of the piezoelectric plate 1 laminate, for positive electrodes and negative electrodes. And the exposure location is set differently. Further, the metal thin plate 2 is desirably smaller than the piezoelectric plate 1 so as not to be exposed on the outer peripheral surface of the piezoelectric plate 1 in order to prevent a short circuit and discharge with the metal thin plate 2 having different polarities.
[0024]
The multi-layer piezoelectric actuator of the present invention is characterized in that, in the above actuator structure, an Ag metal layer 4 substantially not containing glass is deposited on at least both surfaces of the metal thin plate 2. Then, as shown in the schematic view of the joint between the metal thin plate 2 and the ceramic piezoelectric plate 1 in FIG. 4, the Ag metal layer 4 is press-fitted into the gap between the crystal grains 1a on the surface of the ceramic piezoelectric plate 1 to thereby produce the ceramic piezoelectric material. The plate 1 and the thin metal plate 2 can be firmly joined and integrated via the Ag metal layer 4.
[0025]
As the metal thin plate 2, for example, an alloy foil mainly composed of stainless steel or Ni—Fe is used. In particular, an alloy containing Ni-Fe as a main component has high conductivity, and further, a metal such as Kovar (52Fe-31Ni-17Co, 42 alloy (58Fe-42Ni)) close to the thermal expansion coefficient of the piezoelectric plate is used. The thickness of the thin metal plate 2 is preferably as thin as possible so as not to contribute to the amount of displacement, and particularly preferably 20 to 50 μm.
[0026]
If the thickness of the Ag metal layer 4 coated on both surfaces of the thin metal plate 2 is less than 1 μm, the contact strength of the Ag metal layer 4 to the surface of the ceramic piezoelectric plate 1 tends to be insufficient, and the bonding strength may be lowered. Further, if the thickness is larger than 20 μm, the Ag metal layer 4 may inhibit the displacement of the actuator. Therefore, the thickness of the Ag metal layer is preferably 1 to 20 μm, particularly preferably 2 to 15 μm.
[0027]
In general, the Ag metal layer 4 in the present invention can be formed by coating the surface of a metal thin plate by a plating method or a vapor deposition method, or by using a clad material obtained by simultaneously rolling a metal thin plate between two Ag foils.
[0028]
According to the present invention, the Ag metal layer 4 may be formed on both surfaces of the thin metal plate 2 and may be formed on the surface of the connecting member 3 that connects the thin metal plate 2. In that case, the oxidation of the connection member 3 at the time of heat treatment at 400 to 600 ° C. at the time of thermocompression bonding can be suppressed, and a decrease in strength can be prevented.
[0029]
Further, as shown in FIG. 1, an inert body 5 that is piezoelectrically inactive and transmits mechanical energy is made of glass or the like on the uppermost surface and the lowermost surface of the laminate of the ceramic piezoelectric plate 1 and the metal thin plate 2. It is joined to the thin metal plate 2 located on the uppermost surface by the adhesive.
[0030]
The multilayer piezoelectric actuator of the present invention is manufactured by the following method. First, the ceramic piezoelectric plate 1 is formed, for example, by forming a piezoelectric composition mainly composed of Pb (ZrTi) O ₃ (hereinafter abbreviated as PZT) into the shape of each piezoelectric plate 1 and firing at a temperature of 1100 to 1300 ° C. It is produced by doing.
[0031]
On the other hand, the metal thin plate 2 is produced in a predetermined shape as shown in FIG. 3 by punching a metal plate made of a predetermined metal. Thereafter, the surface of the thin metal plate 2 is coated with an Ag metal layer by plating or vapor deposition as described above, or a clad material is used.
[0032]
Then, as shown in FIGS. 1 and 2, the ceramic piezoelectric plate 1 manufactured as described above and the positive and negative metal thin plates 2 on which the Ag metal layer 4 is deposited are formed as shown in FIGS. After the metal thin plates 2 are alternately sandwiched and laminated between the ceramic piezoelectric plates 1 so that the two connecting portions 4 are in the same position every other layer, a load is applied from above and thermocompression bonded.
[0033]
It is important that the load at this time is 700 to 2000 kgf, particularly 700 to 1000 kgf. As is clear from the examples described later, when the load is smaller than 700 kgf, the ceramic piezoelectric plate and the metal thin plate are firmly fixed. However, if the bonding is not obtained and exceeds 1000 kgf, a strong bonding is obtained, but problems such as cracking of the ceramic piezoelectric plate occur.
[0034]
Furthermore, the temperature at this time is suitably 400 to 700 ° C, particularly 450 to 650 ° C. This is because when the temperature is lower than 400 ° C., good bonding strength cannot be obtained, and when the temperature is higher than 700 ° C., the strength of the metal thin plate is lowered and the reliability of the extraction electrode of the metal thin plate is lowered. .
[0035]
By thermocompression bonding under the above conditions, the ductility of the Ag metal layer allows press-fitting between the crystal grains on the surface of the ceramic piezoelectric plate 1 as shown in FIG. The thin plates 2 can be reliably connected to each other.
[0036]
Further, the inactive body 5 installed on the uppermost surface and the lowermost surface of the laminate is 400 to 400 by a lead borosilicate glass or the like at the same time as or after the joining and integrating process of the ceramic piezoelectric plate and the metal thin plate. The inert body 5 is laminated and integrated on the top and bottom of the laminate by baking at 600 ° C.
[0037]
In the laminated piezoelectric actuator laminated and integrated as described above, the outer peripheral surfaces of the ceramic piezoelectric plate 1 and the connecting member 3 are covered with an insulating silicon resin 6 or the like. Similarly, the gap between the outer peripheral portion of the plate 2 and the connecting portion 4 is filled with the insulating silicon resin 6 so that no gap is generated.
[0038]
As such a resin filling method, it is only necessary to adjust the conditions such as the viscosity and fill the voids with an insulating silicon resin under reduced pressure such as vacuum degassing. The insulating silicon resin 6 is desirably filled with a material having a low elastic modulus.
[0039]
【Example】
Example 1
Both sides of the PZT piezoelectric ceramic were polished to produce a disk-shaped ceramic piezoelectric plate 1 having a diameter of 20 mm and a thickness of 0.3 mm.
[0040]
A metal plate made of Kovar having a thickness of 30 μm was punched into a metal member in which 50 metal thin plates made of a circle having a diameter of 19 mm as shown in FIG. 3 were connected by a connecting portion having a width of 2 mm and a length of 2 mm. . Then, an Ag plating layer 5 having a thickness of 5 μm was formed on both surfaces of the metal member.
[0041]
Then, among the above metal members, a circular thin metal plate is sequentially sandwiched between ceramic piezoelectric plates, and a positive metal thin plate and a negative metal thin plate are alternately laminated between the piezoelectric layers of the 99 layers of piezoelectric plates. Formed body.
[0042]
In addition, a PZT ceramic similar to the ceramic piezoelectric body was used as the inert body, and both surfaces thereof were polished to form a cylindrical inactive body having a diameter of 20 mm and a thickness of 5 mm. A glass paste of lead borosilicate glass was printed on one surface of these inert materials to a thickness of 10 μm, dried at 100 ° C., and baked at 500 ° C.
[0043]
In the state where light pressure was applied to the laminated body produced as described above so as not to cause displacement, a load of 1000 kgf was applied from the top with a press machine and pressure bonded at 500 ° C. for 1 hour.
[0044]
Thereafter, the laminated body is entirely covered with insulating silicon rubber, and this is subjected to a polarization treatment by applying a DC voltage of 3 kv / mm for 30 minutes in silicon oil at 80 ° C. to obtain the laminated piezoelectric actuator of the present invention. Produced.
[0045]
Also, after printing a conductive paste of 97% by weight of Ag powder and 3% by weight of glass mainly composed of PbO—SiO ₂ —B ₂ O ₃ on both surfaces of the ceramic piezoelectric plate so as to have a thickness of 10 μm, 100 A ceramic piezoelectric plate was produced by drying at 500 ° C. and baking at 500 ° C. to form a conductive adhesive layer. Then, a comparative piezoelectric actuator was manufactured in the same manner as described above except that this ceramic piezoelectric plate and the metal thin plate 3 made of Kovar were laminated and thermocompression bonded at 500 ° C. for 1 hour.
[0046]
As a result of observing the bonding state of the ceramic piezoelectric body and the metal thin plate with the scanning electron microscope for the four types of laminated piezoelectric actuators obtained, the product of the present invention has an Ag plating layer between the crystal particles on the surface of the ceramic piezoelectric plate. It was confirmed that it was press-fitted and bonded firmly.
[0047]
Next, in order to compare the durability of each sample, a set voltage to be applied to each stacked piezoelectric actuator is obtained so that the generated displacement is 50 μm under an applied load of 440 kgf, and set from the applied load of 440 kgf and the applied voltage of 0 V. An endurance test was performed in which a voltage was applied 1 × 10 ⁹ times at a frequency of 50 Hz. The displacement is measured by fixing the sample on a vibration isolation table, attaching an aluminum foil to the top of the sample, and evaluating the average value of the values measured at the central part and the peripheral part of the element with a laser displacement meter. did.
[0048]
Further, regarding the layer structure in each actuator, one piezoelectric body was sandwiched between a pair of thin metal plates, and a voltage was applied between the thin metal plates to measure a voltage when a spark was generated between the thin metal plates as a withstand voltage.
[0049]
As a result, it was confirmed that the product of the present invention was driven without problems even at 1 × 10 ⁹ times. Further, the withstand voltage was as high as 15 KV / mm. Furthermore, as a result of observing the bonding interface between the thin metal plate and the piezoelectric plate, it was confirmed that the Ag metal layer was press-fitted between the crystal particles on the surface of the piezoelectric body and was firmly bonded.
[0050]
On the other hand, in the laminated piezoelectric actuator that was thermocompression bonded to the metal thin plate made of Kovar through the conductive adhesive layer containing the comparative glass, the driving was stopped at 2 × 10 ⁸ times. The withstand voltage was 11 KV / mm, which was lower than the product of the present invention. As a result of observing the interface between the thin metal plate and the piezoelectric body of this actuator, diffusion of the glass component was observed. Further, as a result of observing the damaged portion of this actuator, it was confirmed that sparking occurred between the conductive adhesive layers formed on the piezoelectric body. Furthermore, as a result of cross-sectional observation in the vicinity of the damaged part, it was confirmed that the piezoelectric plate was cracked starting from the outermost peripheral portion at the joint interface between the thin metal plate and the piezoelectric plate. This phenomenon was observed not only in the damaged part but also in most piezoelectric plates.
[0051]
Example 2
FIG. 5 shows the relationship between the applied load at the time of thermocompression bonding and the bonding strength between the ceramic piezoelectric plate and the metal thin plate when producing the product of the present invention of Example 1. In this test, 70 sheets of a 14 mm diameter, 0.5 mm thick ceramic piezoelectric plate and a 12 mm diameter, 30 mm thick Kovar metal plate with 5 μm thick Ag plating layer on both sides After laminating and thermocompression bonding with each load, it was determined by three-point bending with a lower span of 30 mm. The result is shown in the relationship between applied load and bonding strength in FIG.
[0052]
As is apparent from the results of FIG. 5, it can be seen that a bonding strength of 35 MPa, which is approximately equal to that of the ceramic piezoelectric plate, is obtained at 700 kgf or more. The bonding strength is almost saturated at an applied load of 1000 kgf or more. However, it was confirmed that, at an applied load exceeding 2000 kgf, stress was concentrated on the outer peripheral portion of the thin metal plate 3 in the ceramic piezoelectric plate 2 and micro cracks were generated in the piezoelectric plate.
[0053]
Therefore, it is understood that the applied load at the time of thermocompression bonding is preferably 700 to 2000 kgf, particularly 700 to 2000 kgf.
[0054]
【The invention's effect】
As described in detail above, in the multilayer piezoelectric actuator of the present invention, after thinly laminating metal thin plates coated with an Ag metal layer on both sides and ceramic piezoelectric plates, thermocompression bonding is performed while applying a load of 700 to 2000 kgf. Thus, the ceramic piezoelectric plate and the metal thin plate can be joined and integrated via the Ag metal layer by press-fitting the Ag metal layer between the crystal grains on the surface of the ceramic piezoelectric plate. Can obtain a bonding strength that can sufficiently withstand handling in the process. Further, since it is not necessary to form a conductive adhesive layer on the piezoelectric plate, the process can be simplified.
[0055]
In addition, since the conductive adhesive layer is not formed on the ceramic piezoelectric plate, the conductive adhesive layer and the metal thin plate that were generated at the time of lamination are not misaligned, resulting in the application of a high load when incorporating into the device. Piezoelectric plates and thin metal plates due to stress concentration at the misalignment between the conductive adhesive layer and the thin metal plate, and radial expansion and contraction in the direction of stacking when driving with high voltage and high frequency Since it is possible to prevent the stress generated at the joints from becoming uneven, it is possible to suppress the occurrence of cracks in the piezoelectric plate.
[Brief description of the drawings]
FIG. 1 is a schematic view of a basic configuration of a multilayer piezoelectric actuator of the present invention.
2 is an enlarged cross-sectional view of a part of FIG.
FIG. 3 is a plan view showing a metal member in which thin metal plates are connected by a connecting member.
FIG. 4 is a schematic view of a bonding interface between a ceramic piezoelectric plate and a metal thin plate in the multilayer piezoelectric actuator according to the present invention.
FIG. 5 is a graph showing a relationship between applied load and bonding strength at the time of thermocompression bonding of a multilayer piezoelectric actuator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ceramic piezoelectric plate 2 Metal thin plate 3 Connecting member 4 Ag metal layer 5 Inactive body 6 Insulating silicon resin

Claims (6)

In the laminated piezoelectric actuator formed by alternately laminating a plurality of ceramic piezoelectric plates and a plurality of metal thin plates, an Ag metal layer substantially not containing glass is formed on the surface of the metal thin plate, A multilayer piezoelectric actuator comprising the ceramic piezoelectric plate and the metal thin plate joined and integrated through the Ag metal layer by press-fitting the Ag metal layer between crystal grains on the surface of the ceramic piezoelectric plate. . The multilayer piezoelectric actuator according to claim 1, wherein the thin metal plate is made of an alloy containing Ni—Fe as a main component. The multilayer piezoelectric actuator according to claim 1, wherein the Ag metal layer has a thickness of 1 μm or more. After alternately laminating a plurality of ceramic piezoelectric plates and thin metal plates with an Ag metal layer substantially free of glass on both sides, heating at a temperature of 400 to 700 ° C. while applying a load of 700 to 2000 kgf The Ag metal layer is press-fitted between crystal grains on the surface of the ceramic piezoelectric plate, whereby the ceramic piezoelectric plate and the metal thin plate are joined and integrated through the Ag metal layer. Method for manufacturing a piezoelectric actuator. The method for manufacturing a multilayer piezoelectric actuator according to claim 4, wherein the metal thin plate is made of an alloy containing Ni—Fe as a main component. The method for manufacturing a multilayer piezoelectric actuator according to claim 4, wherein the thickness of the Ag metal layer is 1 μm or more.

Images